Identification of a key odorant contributing to Muscat aroma of Darjeeling black tea

The aroma of Darjeeling black tea was investigated. An unknown odorant reminiscent of Muscat grape was detected with multidimensional gas chromatography–mass spectrometry/olfactometry, and the chemical structure of the unknown component was successfully identified as 4-methylene-2-(2-methylprop-1-enyl)oxane (i.e. dehydrorose oxide or DHRO), which has Muscat-like and floral notes on its own. The present study is the first to detect DHRO as an odorant in Darjeeling black tea. The odour threshold of DHRO was calculated to be 0.20 μ g/kg in water, and a stable isotope dilution assay showed that the amount of DHRO in a Darjeeling black tea infusion was 0.028 μ g/kg. The odour activity value (OAV) of DHRO in the Darjeeling black tea infusion was 0.14. A sensory evaluation was conducted to obtain the orthonasal aroma profiles of black tea aroma model solutions and revealed the effect of DHRO in Darjeeling black tea. DHRO was found to contribute to the characteristic attributes such as Muscat-like, floral, fruity and green aroma of Darjeeling black tea, although the OAV was less than 1.